[PATCH 0/2] super: convert to a plain hashtable

[Christian Brauner <brauner@kernel.org>]

This sits on top of the superblock fixes for v7.3.

Convert the rhltable to a plain hashtable under a spinlock. The walks
keep their place with a cursor entry in the chain. A claim is unhashed
the moment it's dropped and a walk that finds a superblock that isn't
born yet waits for it to be born or to die and looks again. Since
hashing can't fail anymore the entry for the superblock's own s_dev is
embedded in struct super_block and the preallocation in alloc_super()
goes away. This all simplifies things quite a lot.

It also fixes a btrfs bug where fs_bdev_freeze() ended up freezing a
btrfs filesystem through a stale member that open_ctree() had already
released while the freeze was waiting for SB_BORN. The resume doesn't
find a holder for that device anymore so the filesystem stays frozen
for good.

The selftest freezes a device that several erofs superblocks share.
That's the one case where a device legitimately carries claims from more
than one superblock and it checks that a suspend freezes each of them
exactly once and that mounts coming and going under a suspended device
leave nothing frozen behind.

I modeled the table in TLA+ and checked the real list code with CBMC.
Both agree with the design.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
Christian Brauner (2):
      selftests/filesystems: add a test for freezing a shared block device
      super: convert to plain hashtable

 block/bdev.c                                       |   2 +-
 fs/internal.h                                      |   1 -
 fs/namespace.c                                     |   2 -
 fs/super.c                                         | 332 ++++++--------
 include/linux/fs/super_types.h                     |  11 +-
 .../selftests/filesystems/freeze/.gitignore        |   1 +
 .../testing/selftests/filesystems/freeze/Makefile  |   2 +-
 tools/testing/selftests/filesystems/freeze/config  |   1 +
 .../filesystems/freeze/shared_bdev_test.c          | 479 +++++++++++++++++++++
 9 files changed, 627 insertions(+), 204 deletions(-)
---
base-commit: 16efce55f70b6093dbe53bffb8e79fb0e08a95b6
change-id: 20261011-work-super-dev_hash-e30f79361408